<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>React 状态</title>
<script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script>
<script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
<script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
</head>
<body>

<div id="example"></div>
<!-- 数据自顶向下流动 -->
<script type="text/babel">
function FormattedDate(props) {
  return <h2>现在是 {props.date.toLocaleTimeString()}.</h2>;
}

class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }

  componentDidMount() {
    this.timerID = setInterval(
      () => this.tick(),
      1000
    );
  }

  componentWillUnmount() {
    clearInterval(this.timerID);
  }

  tick() {
    this.setState({
      date: new Date()
    });
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <FormattedDate date={this.state.date} />
      </div>
    );
  }
}

ReactDOM.render(
  <Clock />,
  document.getElementById('example')
);
</script>

</body>
</html>